Plamen Pilarski

Monitoring the establishment and prevalence of the fungal entomopathogen Entomophaga maimaiga in two Lymantria dispar L. populations in Bulgaria

The establishment and prevalence of the entomopathogenic fungus Entomophaga maimaiga, (Zygomycetes, Entomophthorales), introduced into two gypsy moth populations in Bulgaria, was monitored during 2000–2004. In the Karlovo Region population, where E. maimaiga was introduced in 1999, the fungus was recovered every year and the prevalence of infection varied from 6.1% to 15.9%. A microsporidian infection caused by an Endoreticulatus sp. (Protista, Microsporidia) was also recorded every year and the prevalence varied from 2.1% and 5.0%. In the Svoge Region population, where E. maimaiga was introduced in late 2000 and first found in 2002, the prevalence of infection varied from 8.8% to 13.8%. Larval parasitism caused by Cotesia melanoscela, Protapanteles liparidis (Hymenoptera, Braconidae) and species of tachinids (Diptera, Tachinidae) was also recorded in the larvae of both populations. We provide a rationale as to why other countries should consider introducing E. maimaiga for biological control of Lymantria dispar populations.

Introduction of the entomopathogenic fungusEntomophaga maimaiga hum.

The entomopathogenic fungusEntomophaga maimaiga was introduced into aL. dispar population situated in South Bulgaria for the first time in Europe.It was found that of all larvae collected in the five experimental plots, 6.3 % contained conidia and resting spores ofE. maimaiga, 14.2 % contained parasitoids and 2.3 % were infected with nucleopolyhedrovirus (NPV). The presence of the fungus in cadavers collected from each experimental plots and on five of the six collection dates was observed.The entomopathogenic fungusEntomophaga maimaiga was introduced into aL. dispar population situated in South Bulgaria for the first time in Europe.

The potential for Entomophaga maimaiga to regulate gypsy moth Lymantria dispar (L.) (Lepidoptera: Erebidae) in Europe

Gypsy moth, Lymantria dispar L., is one of the most important pests of deciduous trees in Europe. In regular cycles, it causes large‐scale defoliation mostly of oak, Quercus spp., forests. Government authorities in the most infested countries in Europe conduct large‐scale applications of pesticides against gypsy moth. In 1999, a new natural enemy, the entomopathogenic fungus Entomophaga maimaiga, was successfully introduced into a gypsy moth population in Bulgaria. Recent investigations suggest that now E. maimaiga is quickly spreading in Europe. Herein, past studies are reviewed regarding this fungus with special emphasis on its potential for becoming an important factor regulating gypsy moth populations in Europe, focusing on the hosts population dynamics in relation to the fungus, the influence of environmental conditions on fungal activity, the influence of E. maimaiga on the native entomofauna, including other gypsy moth natural enemies, and spread of the fungus. Based on this analysis, the potential of E. maimaiga for providing control in European gypsy moth populations is estimated.

Interactions between the introduced fungal pathogen Entomophaga maimaiga and indigenous tachinid parasitoids of gypsy moth Lymantria dispar in Bulgaria

Interactions between the gypsy moth, Lymantria dispar L. (Lepidoptera: Erebidae), pathogenic fungus Entomophaga maimaiga, and the tachinid parasitoid (Diptera: Tachinidae) complex in gypsy moth larvae were investigated in Bulgaria, where E. maimaiga was recently released as a biological control agent. Gypsy moth larvae were collected in oak stands where E. maimaiga was originally introduced (nine sites) and in sites where the pathogen has invaded by natural extension of the range (ten sites). In total, 4,375 host larvae were examined and 401 tachinid larvae emerged from parasitized hosts. Host mortality caused by tachinids varied from 0 to 48.5% among sites, with an overall average of 9.2%. Emerging adult tachinid parasitoids included 54 individuals belonging to six species: Compsilura concinnata, Exorista larvarum, Senometopia separata, Senometopia excisa, Drino incospiqua and Zenilia libatrix; the remaining parasitoids (86.5%) died in the pupal stage. E. maimaiga azygospores were observed on puparia surfaces, an indication that the gypsy moth host larvae were infected with the fungus. No azygospores were observed in parasitoid tissues. The high parasitoid mortality may be the result of the competition with E. maimaiga during development in the same host.

Мicroscopic investigations (LM, TEM and SEM) and identification of Chlorella isolate R-06/2 from extreme habitat in Bulgaria with a strong biological activity and resistance to environmental stress factors

An extremophilic Chlorella strain R-06/2, isolated from a geothermal spring (+42 °C) in the region of Rupite village (SW Bulgaria), was investigated for species identification. This was done by observation of the cell morphology, reproduction and ultrastructure by light microscopy, scanning electron microscopy and transmission electron microscopy, and by investigation of the cell-wall chemistry. The pyrenoid ultrastructure with a double-layered thylakoid traversing the matrix, the shape of the starch envelope, as well as the cell wall, composed of glucosamine and developed around young autospores, were the features that allowed us to classify the thermophilic strain Chlorella R-06/2 as Chlorella vulgaris Beijerinck 1890.

Growth, biochemical and enzymatic responses of thermal cyanobacterium Gloeocapsa sp. (Cyanophyceae) to temperature and irradiance

The present study describes a strain of Gloeocapsa sp. designated as Gacheva 2007/R‐06/1, originally isolated from a geothermal flow located in Rupite, Bulgaria. To evaluate whether this cyanobacterium is locally adapted to hot environment or has the ability to tolerate lower temperatures, its growth, biochemical composition, enzyme isoforms and activity of the main antioxidant enzymes and proteases were characterized under various temperatures and two irradiance levels. The strain was able to grow over the whole temperature range (15–40°C) under two different photon fluence densities – 132 μmol photons m−2 s−1 (unilateral, low light, LL) and 2 × 132 μmol photons m−2 s−1 (bilateral, high light, HL). The best growth occurred at either 34°C and LL or at 36°C and HL, but significant growth inhibition was noted at 15°C and 40°C. Low temperature treatment (15°C) resulted in higher levels of total protein and an increased activity of manganese superoxide dismutase (MnSOD) and glutathione reductase, as compared to optimum growth temperatures. After simultaneous exposure to 15°C and HL, increases in lipid content and activity of iron superoxide dismutase and catalase (CAT) were also observed. Cultivation of cells at 40°C enhanced MnSOD, CAT and peroxidase activities, regardless of irradiance level. Increased total protein content and protease activity at 40°C was only associated with the HL treatment. Overall, these results indicate that Gloeocapsa sp. strain Gacheva 2007/R‐06/1 used different strategies to enable cells to efficiently acclimate and withstand adverse low or high temperatures. This strain obviously tolerates a wide range of temperatures below its natural habitat temperature, and does not seem to be locally adapted to its original thermal regime. It behaved as a thermotolerant rather than a thermophilic cyanobacterium, which suggests its wider distribution in nature.

POTENTIAL OF ENTOMOPHAGA MAIMAIGA HUMBER, SHIMAZU AND SOPER (ENTOMOPHTHORALES) FOR SUPPRESSING LYMANTRIA DISPAR (LINNAEUS) OUTBREAKS IN BULGARIA

The Asian fungal entomopathogen Entomophaga maimaiga was first introduced in Bulgaria for biological control of gypsy moth, Lymantria dispar, in 1999 and the first epizootics in gypsy moth populations were observed in 2005. Six introductions of E. maimaiga in oak forests with heavy L. dispar infestations were conducted from 2008 to 2011 in different regions of the country, including Nova Zagora, Gorna Oryahovitsa, Popovo, Targovishte and Staro Oryahovo. As a result of these introductions, host density was decreased by 55.1–100% and the outbreaks were suppressed. After the introduction of the pathogen in Bulgaria, no microbiological or chemical control of L. dispar has been necessary and the last two gradations have been estimated to be 15–30% of the values in previous gradations.

Evaluation of the Acute Toxicity of the Herbicide Stomp 33EC (Pendimethalin) with a Test Object Chlorella Kessleri

ABSTRACT An acute 96-hours experiment, in three repetitions, with the herbicide STOMP 33 EC has been carried out with Chlorella kessleri. Toxic criteria—inhibition of the growth rate. The statistically averaged dependency of the preparations toxicity from the concentration and time is given analytically. EC5, EC50, EC95 for 24, 48, 96h and the probable harmless concentration have been established. A lot of morphological changes such as: cells loss color, retaining of the cell division, conjugants, to strongly injured, yellowish cells with empty content, as well as completely destroyed algal cultures at the high concentrations, were registered.